The present invention relates to a method and to a device for measuring a battery cell current.
Current battery systems are constructed from a plurality of battery cell control units comprising respectively one battery cell, whereby an individual control of the individual battery cells connected to the battery cell control unit is made possible. The battery cells are connected to one another in a series circuit via the battery cell control units. Furthermore, a central control unit for controlling the battery system is present.
In order to generate a controlled total output voltage of the battery system, individual battery cells are inserted with the aid of the battery cell control units into the series circuit either with positive or negative polarity, relative to the tap of the total output voltage, (condition: “connected with positive polarity” or “connected with negative polarity”); or said individual battery cells are switched off, i.e. are separated from the series circuit and the connection terminals of the associated battery cell control unit are connected in an electrically conductive manner (condition: “bypassed”).
In addition, the battery system is controlled in such a manner that battery cells are activated as a function of the state of charge thereof and of further state variables (e.g. SOH—state of health), whereby an active balancing of the battery cells is made possible.
The SOH can be determined on the basis of the current cell voltage and the energy already withdrawn, which is possible with the aid of a current sensor. Because each battery cell can be actuated independently of the other battery cells in such a battery system, each battery cell requires an option for determining the charging/discharging current with which said cell is currently being charged/discharged. The current measurement can, e.g., be carried out on each of the battery cell control units by means of a shunt resistor measurement or a Hall sensor.
A battery system or respectively a battery 60 according to the prior art is shown in FIG. 6. The battery system 60 comprises a plurality of battery cell control units 61 connected in series (also referred to as smart cell units). Each battery cell control unit 61 comprises a battery cell 64. The battery cell control units 61 are connected to a central controller 63 via a unidirectional communication interface 62. The battery cells 64 of the battery cell control units 61 can be individually inserted into a series circuit of all the battery cells 54 or bypassed in said series circuit by means of a control signal from the central controller 63 via the unidirectional communication interface 62.